1. Field of the Invention
The invention relates to the selective removal of nitrogen oxides from gas streams. More particularly, the invention relates to the selective removal of nitrogen oxide from combustion effluent gas streams by contacting said stream with sulfur.
2. Description of the Prior Art
Combustion effluents and waste gas streams have been shown to be a major source of air pollution when discharged into the atmosphere. As clearly evidenced in the Los Angeles area, unless the waste gas streams are treated to remove deleterious components, serious smog problems can develop. One of the major irritants in smog is NO.sub.2. A major source of NO.sub.2, in turn, is the formation of NO by combustion processes. These combustion processes include stationary sources such as power plants, process furnaces, incinerators, and the like, as well as automobiles. The NO.sub.x formed by combustion is generally discharged into the atmosphere as NO and only subsequently converted to NO.sub.2.
A number of different processes for the selective removal of NO from effluent gas streams have been proposed. One process, disclosed in many patents including U.S. Pat. Nos. 3,864,451, 3,900,544, and 4,164,546, involves the injection of ammonia in effluent gas streams. A variety of other processes, including both wet and dry processes, are described in "Survey and Analysis of Flue Gas Treatment Methods", Engineering-Science, prepared for American Gas Association, AGA Catalog No. L51386, pp. II-10 to II-18. All of these processes have certain deficiencies which have prevented their use in large-scale treatment.
A new process for the selective removal of NO from effluent gas streams has been discovered which has potential for large-scale application.